text: Sand closures involve employing a dumping capacity within the closure gap that introduces more material per tidal cycle than can be removed by the current. Unlike stone closures, the material used here is inherently unstable under the flow velocities encountered. Typically, sand closures do not necessitate soil protection. This, among other reasons, makes sand closure a cost-effective solution when locally sourced sand is utilized. Since 1965, numerous tidal channels have been effectively sealed using sand, aided by the rapidly increasing capabilities of modern sand suction dredgers.
  These advancements have enabled quick and voluminous sand delivery for larger closures, tolerating sand losses during the closing phase of up to 20 to 50%. The initial sand closures of tidal channels — including the Ventjagersgatje in 1959 and the southern entrance to the Haringvliet bridge in 1961 — contributed to the development of a basic calculation method for sand closures. Subsequent sand closures provided practical validation for this method, refining predictions of sand losses.